Its Daves blog not mine but yes we are aware of the issues with GPS interference (Someone mentioned it on the GPSL list which explained the loss of my first payloads GPS). Dave is still mad at me for sticking a MDS 90 camera to his payload once and breaking it. Due to the lack of time for testing we flew 2 other trackers on the balloon just to be sure. I think Dave plans to have more shielding next time (we are developing a board with an external antenna for the GPS and utilising the uBlox 6 chip). Its worth noting for the record that the AEE MDS-90 also easily jams the latest uBLOX 6 modules with passive antennas however the GoPro's don't jam the signal.
On Mon, Jul 23, 2012 at 6:21 PM, Barry Sloan <barry2@...>
A few comments after checking out your : http://www.daveakerman.com/?p=592 link.
You mention having GPS problems due to interference and from one of the images it appears you were using a Trimble Lassen iQ GPS receiver which from my experience is very poor in this respect. After unsuccessfully getting my first iQ receiver to function I figured it must be defective and ordered another from a different supplier, but ended up buying 2 more before using my laptop to test them and discovering that they were all OK, except when within 15-20 feet of the PC that I had been using and which was used to test all the other GPS receivers I have without any problems. I was hoping the problem was limited to some specific frequency the PC emitted, but after experiencing problems using the iQ on several flights with different cameras set the iQ receivers aside and now use Copernicus receivers. I was going to add that it was just as well that the switching regulators you ordered didn’t arrive in time for the flight as most generate terrible RFI for GPS receivers, but in your case the GPS had already failed so they could have likely been used OK without any further problems. Digital cameras and anything else digital all generate RFI and even though things appear to be ok on the ground, we’ve had problems several times after things were airborne due to RFI frequencies changing due to temperature and/or battery voltages changes which is why we now always use a second tracker in a separate enclosure away from all the RFI generating devices. Anyway, just figured I’d pass on my experiences with the iQ in case they help avoid future problems.
From: GPSL@yahoogroups.com [mailto:GPSL@yahoogroups.com] On Behalf Of Anthony Stirk
Sent: Monday, July 23, 2012 9:01 AM
To: Mike Manes
Cc: GPSL Balloon Reflector; EOSS membership reflector; David Akerman
Subject: Re: [GPSL] Raspberry Pi used as flight computer aboard black-sky balloon • The Register
Not sure on the exact power but it was running 6 x AA Energizers and was very hot when it got back http://www.daveakerman.com/ did the Pi payload. It was on the ground for 30 mins in the sun too which probably didn't help. Insulation was as thin as possible whilst having the structural strength to hold it all in :
We will probably put the heat sinks outside next time :) Anyway I can confirm the Pi isn't a great tracker.
I think my Government have more important things on their plate at the moment than our silly radio laws, its worth nothing we can apply (full license holders anyway) for a Notice of Variation to the license to allow us to use different modes/ more power/airborne use however no one has done it yet (For HAB anyway). Personally I feel the restrictions force people to be more inventive, our distributed network of listeners really really helps. APRS backup would be nice but as you aren't allowed to leave an unattended station transmitting in the UK APRS hasn't been widely taken up so it probably wouldn't be worth it even if it was legal to transmit from the air.
On Thu, Jul 19, 2012 at 10:25 PM, Mike Manes <mrmanes@...> wrote:
Your piece didn't mention how much power the Pi processors dissipated, but it seems you concerns re impaired free convective heat transfer
were quite valid. Those added heatsinks simply added thermal mass,
but without an air mass flowing, any heat extraction would have been
mainly via radiation; and that's how spacecraft dump heat: into the
blackness of space. So that's how your heatsinks should be designed,
with high emissivity at your max allowable chip case temperature.
Just make sure that the heatsinks can "see" a cold surface and not
get hit by solar flux.
I also suspect that you went overboard on thermal insulation. Our
payloads dissipate a total of 3-4 W over numerous assemblies, and
our thermal insulation is just 3mm of foam core board. Since latex
flights are only a few hours and typically in daytime, the resident
thermal mass also helps a lot. The lowest internal temp we've seen
is about -10C, and that's just transient.
I hope you guys in Ol' Blighty can get your MPs to pass regulations
that exempt unmanned aircraft from the ham radio ban, consistent with
the rest of the ARHAB world.
73 de Mike W5VSI
On 7/18/12 11:51 PM, Anthony Stirk wrote:
It was a launch Daveake and I did this weekend (the Pi payload was
Daves). We also did a Pico launch up to 43km+. The Pi doesn't make a
good tracker and was extremely hot when it returned, it had actually
melted the packing and people think we need hand warmers :) That said
with our very restrictive radio laws getting live images back is a feat
in itself but thanks to our amazing volunteer trackers I don't think we
lost hardly any of the image data.
Dave's write up is here : http://www.daveakerman.com/?p=592
And mine is here : http://ava.upuaut.net/?p=315
On Thu, Jul 19, 2012 at 4:37 AM, Mike Manes <mrmanes@...